This invention relates in general to impact printers and more particularly it relates to impact printers having a print ribbon and a separate erase ribbon.
In various printers including typewriters such as those manufactured by IBM and SCM, the platen which supports the print receiving medium in the impact printing position remains stationary and the character printing elements move along the platen on a carriage to various printing locations. The character elements may be mounted on a ball or on a wheel oftentimes referred to as a daisy.
In those printers in which the characters are mounted on a ball, the erase ribbon has typically been positioned between the print ribbon and the platen. Thus, when the printer is operated in the print mode, each time a character is formed the print ribbon is elevated from its rest position to its print position while the erase ribbon remains stationary. When the printer is operated in the erase mode, the erase ribbon is raised and the print ribbon remains stationary. While this arrangement operates adequately in printers using a ball type character element, it has not been adaptable to printers using a daisy type character element. The nature of the daisy type character elements is such that they must be positioned closer to the platen than with ball type character elements, and accordingly there is not sufficient clearance to permanently position two ribbons, i.e., both the print and the erase ribbon between the daisy and the platen. Further, even if the erase and print ribbons could be placed in such a side-by-side relationship between the daisy and the platen, this arrangement would tend to increase the distance that the printer's hammer would travel before the daisy would strike the platen. In order that printers can be adaptable to operate at extremely high speed, it is desirable to keep the length of the hammer stroke to a minimum.
Another erase ribbon mounting arrangement is that disclosed in U.S. Pat. No. 3,595,362 to Wolowitz. Disclosed therein is a single print ribbon having two tracks thereon, the top track being the print track and the bottom track being an erase track. While this type of ribbon would eliminate the space disadvantages of using two separate ribbons in a daisy type printer, other disadvantages are presented. For example, the cost of manufacturing ribbon which contains two separate tracks of different types far exceeds the cost of manufacturing separate erase and printer ribbons. Further, since as a general rule, a printer operates in the print mode far more frequently than it operates in the erase mode, large amounts of erase ribbon remain unused when combination print/erase ribbons are used.